Existing pipe couplings have a gripping device disposed on the inner surface of the coupling housing so as to compress the gripping device against the pipe to secure the end of the pipe. The gripping device is typically secured to the housing with an adhesive or a pin to hold the gripping device in place prior to installation of the coupling to the pipe end and afterward when the coupling is removed and reinstalled. In particular applications, for example, pipe couplings are commonly installed and reinstalled as piping systems are assembled, disassembled, and reassembled when relocating or rerouting the piping system.
Both of the above-described securing methods, using an adhesive or a pin, involve connecting a first member (the gripping device) to a second member (the housing) with a third member (the adhesive or pin) that interacts with the first and second members. In both methods, the structure of the third member is disposed between the first and second members and communicates forces between the first and second members through the structure provided by the third member. The surfaces of the third member also engage the surfaces of the first and second members to communicate forces between the first and second members through these surfaces.
When adhesive is used to secure the gripping device, a layer of the adhesive is disposed between the housing and the gripping device and the forces applied by the housing to the pipe end are communicated through the adhesive layer to the gripping device and then to the pipe. Also, the surfaces of the adhesive layer engage the housing and the gripping device with an adhesion strength that is dependent on the characteristics of the adhesive and on the characteristics of the mating surfaces. It is believed that forces applied to the adhesive layer can undesirably weaken the adhesive layer over time, and that environmental factors such as temperature-induced stresses or dirt can further weaken the structural properties of the adhesive. It is also believed that the surfaces of the adhesive layer can be weakened due to the transmission of forces through the mating surfaces of the adhesive, housing, and gripping device and through the effects of the same environmental factors. Furthermore, it is believed that the repeated application of force to the coupling due to the repeated reinstallation of the coupling to a pipe system further weakens the adhesive and the adhesion of the adhesive to the housing and gripping device over time. The degradation of the adhesive layer or of the adhesive layer adhesion properties is believed to undesirably cause the gripping device to disengage from the coupling.
When a pin is used, the pin is disposed to extend between mating holes of the housing and gripping device. Forces applied by the housing are partly communicated through the pin and partly communicated directly to the gripping device. It is believed that forces applied to the pin over time can cause the pin to deform, loosen, or move out of position from the mating holes, thereby permitting the gripping device to undesirably disengage from the coupling. The repeated installation and reinstallation of the coupling is also believed to further apply stresses to the pin and can cause the pin to move out of position. The failure of the pin to maintain position is believed to undesirably cause the gripping device to disengage from the coupling, thereby preventing reinstallation of the coupling to a piping system. Furthermore, the installation of the pin requires a pin-receiving hole to be drilled that could extend through the housing to the channel of the housing that holds the gasket for the pipe coupling assembly. It is believed that a pin disposed in such a hole and extending in part into the channel can contact the gasket and possibly damage the gasket if a sharp edge of the pin end contacts the gasket.
When an adhesive or pin is used, it is believed that the thickness of the adhesive layer or placement of the pin does not permit the gripping device to fully compress against the housing, or bottom out, as would be achieved without the presence of the adhesive layer or pin. Namely, it is believed that the mating surfaces of the gripping device and housing deform when compressed during coupling installation, which causes the gripping device to deform the housing slightly and thereby redistribute forces to structures opposing the compression, such as an adhesive layer or a pin placed before the application of the compressive force. It is further believed that the repeated application of such forces to the adhesive or pin over time cause the adhesive or pin to degrade, weaken, or deform, thus permitting the gripping device to disengage from the coupling when the coupling is repeatedly removed from or readjusted on the pipe ends.
Some existing gripping devices have a single bend disposed between two straight portions of the gripping device, which presents two straight surfaces to the pipe ends when the gripping device is compressed against a pipe. This is believed to disadvantageously limit the amount of contact between the gripping device and the pipe, and to thus reduce the strength of the pipe coupling.